The present invention relates to a centrifuge instrument, and more particularly, to a centrifuge in which a rotor hold-down screw, a nut and a spring are arranged to secure a rotor to a drive cone.
A centrifuge instrument is a device by which a liquid sample may be subjected to a centrifugal force that separates the liquid sample into its constituent parts. The sample is typically carried in a tube situated within a member known as a centrifuge rotor. The rotor is mounted on a drive cone, which is connected to a drive shaft that provides a source of motive energy to rotate the rotor.
The centrifugal force that advantageously acts upon the sample also acts upon the rotor that holds the sample. If the rotor separates from the drive cone during centrifuge operation, it could damage the centrifuge instrument. If the rotor is thrown from the centrifuge instrument, it could damage external equipment or injure a person in the vicinity of the instrument. Accordingly, the rotor must be adequately secured to the drive cone.
The mounting of the rotor to the drive cone is typically accomplished by way of a rotor hold-down screw. A central region of the rotor rests upon the drive cone. The rotor hold-down screw is routed through a cover hold-down screw knob and the central region of the rotor, and tightened into a threaded channel in the drive cone. That is, the rotor hold-down screw is threaded directly into the drive cone. To better secure this arrangement, a lock washer is sometimes placed between a lower surface of the rotor hold-down screw and an upper surface of the cover hold-down screw knob.
As compared with an older centrifuge instrument, a newer centrifuge instrument typically has a stronger motor, better drive design, and a more powerful refrigeration system. These features of the newer instrument provide the operator with the advantages of faster acceleration and deceleration, an ability to run the rotor with a greater degree of imbalance, and a possibility of having a colder rotor chamber temperature.
The centrifuge instrument may accept any one of a plurality of different centrifuge rotors depending upon the separation protocol being performed, and it is not uncommon for an operator to use an old rotor on a new centrifuge instrument. However, the capability of the new instrument to more rapidly change its speed and temperature, and to operate with a greater degree of imbalance, also increases the chance for the rotor hold-down screw to become loosened, and thus increase the opportunity for the rotor to become separated from the drive cone.
The present invention provides an improved arrangement for securing a rotor to a drive cone in a centrifuge instrument, and is suitable for an environment in which the centrifuge speed or temperature are rapidly changed.
An apparatus for securing a rotor to a drive cone in a centrifuge includes (a) a nut, movable in an axial direction in the drive cone, (b) a screw, for passing through a region of the rotor and for engagement with the nut, and (c) a spring located between a surface of the nut and a surface of the drive cone. The screw, when tightened into the nut, moves the nut in the axial direction to compresses the spring between the surface of the nut and the surface of the drive cone. The nut may include a protrusion that fits into a slot in the drive cone to limit rotation of the nut with respect to the drive cone. The spring can be any of a double-spring washer, a compression spring, a disc spring or a belleville spring washer.
The apparatus can also include a retaining ring for holding the nut and the spring in the drive cone. Such a retaining ring is located adjacent to a perimeter region of the nut, within an annular groove of the drive cone.
A preferred embodiment of the present invention is an apparatus for securing a rotor to a drive cone in a centrifuge, where the apparatus includes (a) a nut, movable in an axial direction in the drive cone, (b) a screw for passing through the rotor and for engagement with the nut, (c) a spring located between a surface of the nut and a surface of the drive cone, and (d) a retaining ring for holding the nut and the spring in the drive cone. The retaining ring is located adjacent to a perimeter region of the nut, within an annular groove of the drive cone. The screw, when tightened into the nut, moves the nut in the axial direction to compress the spring between the surface of the nut and the surface of the drive cone. The nut has a protrusion that fits into a slot in the drive cone to limit rotation of the nut with respect to the drive cone.